Note that if said person finds 90mg/day of adderall xr to be ineffective, 70mg of vyvanse (~30mg of dextroamphetamine) isn't going to do a whole lot.
To the OP: If you want an adderall IR type effect, simply crush the beads with a pill crusher into a powder and place inside a capsule.
This is a way better solution then messing with RC stimulants, which are potentially impure and of unknown safety.
The best RC stimulant for this purpose would be 2-FMA, hands down. Problem is, 2-FMA is of unknown toxicity. At the very least, the long half-life makes its a potential cardiovascular risk. It might also be hard on the liver and possess other toxic properties like 4-FMA. I like 2-FMA and feel like its worth the risk to take sometimes but it definitely doesn't feel like something you'd want to take daily. Additionally, 2-FMA is fairly pricely and not extremely potent, so if you need 90mg/day of adderall you're going at least the same amount of 2-FMA. We can't tell you where to get it, and again, I don't recommend it.
Again, my advice is just to crush the adderall.